Precision honing machine

ABSTRACT

A honing machine for rods of stepwise varying diameters having sensors for sensing the diameter and controlling magnetic valves for hydraulically moving the honing members into and out of engagement with a workpiece. The sensors are contact-free magnetic circuits, the reluctance of which depends on the degree of proximity of a workpiece so as to variably couple a current source to circuits for actuating the valves.

United States Patent Schmidt [45] Apr. 11, 1972 54] PRECISION HONING MACHINE [56] References Cited [72] Inventor: ghomas Schmidt, Munchingen-Kallenberg, UNITED STATES PATENTS ermany 2,195,049 3/1940 Wallace ..51/59 R [731 Asslgnw 22 wieck Hutu", 2,327,022 8/1943 Dall et a].

2,998,676 9/1961 Hawkins ..51/59 R x [22] Filed: June 25, 1970 [21 1 App]. No: 49 715 Primary Examiner-Lester M. Swingle Attorney-Edwin E. Greigg [30] Foreign Application Priority Data [57] ABSTRACT June 30, 1969 Germany ..P 19 33 106.7 A honing machine for rods of Stepwise varying diameters ing sensors for sensing the diameter and controlling magnetic ((IIII ..51/66, 3124: valves for hydraulically moving the honing members into and [58] Field o'i'szsi'e'i; 3]]661391136519, 165.91, engagement with a mkpiem The Sens are 5 5 92 free magnetic circuits, the reluctance of which depends on the degree of proximity of a workpiece so as to variably couple a current source to circuits for actuating the valves.

11 Claims, 6 Drawing Figures PATENTEDAPRH I972 3,654,737

sum 1 or 2 IN VEN TOR.

PRECISION I-IONING MACHINE FIELD OF THE INVENTION The invention relates to a machine for high-precision honing of workpieces of rod shape exhibiting a stepwise variation in diameter.

lt is previously known to provide in a high-precision honing machine a pair of rollers rotating in the same sense and having tangential contact in the longitudinal direction with rodshaped workpieces supported thereby, feeding movements being imparted to the workpieces owing to the disposition of the rollers in separate planes defining an acute angle and intersecting along a line which is perpendicular to the axes of the rollers, honing members being reciprocable in the axial direction of the workpieces and engaging the sections of largest diameter thereof. Sensor means respond to sections of the workpieces of smaller diameter to increase the distance of the honing members from the axis of the workpiece when such sections pass in front of the honing members.

Conventional machines are provided with mechanical sensors having resilient contact with the rotating workpieces so as to respond when a step or shoulder passes under the sensor indicating the transition to another value of the diameter. The sensors then initiate a control process causing the honing member supports to be raised or lowered by means of magnetic valves or the like.

Since it is not possible for reasons of space to locate the sensors below the workpiece, they are positioned between a pair of honing members, as a consequence of which the moment at which the sensor passes over the diameter step does not coincide with the moment at which the honing member should be raised or lowered. To remove this drawback, arrangements have been provided for storing the signal for initiating the raising or lowering of the honing members with a delayed response. Such arrangements are very complicated because the delay has to be adjusted with extreme accuracy. Even if the theoretically required delay is realized with an extraordinarily small tolerance, it is not possible to achieve perfect operation, since the honing members, which have to be of substantial height in order not to require too frequent exchange, depending on the extent of wear thereof, have to move by different amounts from the raised position into contact with the workpiece. This causes the time required for the control signal to bring about the contact with the workpiece to vary. These time variations are far from negligible in view of the fact that the honing members must be lowered slowly in order to avoid breakage when they impinge on the workpiece. This factor is more important the higher the rate of feed.

It is imperative to control with the utmost precision the point at which the honing member engages the workpiece in order to retain the geometrical form at the transition from a larger to a smaller diameter, which is not possible with the prior arrangements referred to. Furthermore, if sensors in cooperation with delay devices are used in high-precision machines, which usually require a large number of honing members, such as eight or 10, and two delay devices for each honing member, the resulting arrangement is extremely com plicated and costly. Also, there is danger of damage to the surface of a workpiece from the rotating members of the sensors, which have to participate in the rotation of the workpieces and in the feeding movement thereof. The resulting wear on these rotating members is substantial. It is also very unfavorable from the operators point of view that the delay devices have to be readjusted subsequent to a change in the rate of feed.

SUMMARY OF THE INVENTION According to the invention, the drawbacks of the prior machines are removed through the use of contactless sensors operating, for instance, on the inductive or the magnetic principle, the sensors being positioned below the sections of workpieces covered by the honing members and opposite to the latter so as to be at a small distance from sections of the workpieces having the largest diameters, the sensors being fixed in position and being adapted to respond electromagnetically for controlling disengagement of the honing members from the workpiece.

Owing to this positioning of the sensors, the moment at which an impulse is applied to the magnetic valve coincides practically completely with the moment at which the honing members are raised or lowered, so that no delay devices are required. Since the sensors do not contact the workpieces, they are not subject to wear and cannot cause damage to the workpiece. No complicated adjustment of delay devices for changing the rate of feed is necessary. Since the control device operates electrically, the response is practically instantaneous. The cost of the arrangement is substantially lower than that of mechanically operated sensors.

If the requirements with regard to the geometrical shape of the steps of the workpieces at the transitions from a higher to a lower value of diameter are not exceedingly stringent, the sensors can be positioned below the midpoints of the sections of the workpieces covered by the honing members. In the simplest form of a honing machine according to the invention with one sensor per honing member, each sensor cooperates with a corresponding relay having a contact which is inserted in the current supply circuit of a magnetic valve controlling the pressure medium for operating the honing members. Owing to the positioning of the sensors below the midpoints of the honing members, the latter engage or disengage the workpiece as soon as a step or shoulder thereof arrives at the midpoint of the honing member. At the moment when the honing member contacts the workpiece, only one-half of the honing member, as measured in the longitudinal direction, is operative and before disengagement occurs the effective length of the honing member is again reduced to one-half. As a result of this, the profile of a finished workpiece close to the end of a honed section tapers off towards the step, corresponding to a decrease in diameter. This phenomenon is particularly pronounced when a so-called inductive sensor is used under the midpoint of the honing member, this type of sensor being particularly suitable for this application owing to its small dimensions.

To obviate this geometrical deficiency in the workpieces, it is necessary for a larger portion of the length of the honing member to be operative at the moment of engagement or disengagement, i.e. the honing member must not extend appreciably beyond the step and under no conditions as much as by one-half of its length. The permissible amount of such extension can only be ascertained by practical tests.

This mode of operation can be achieved with the aid of inductive sensors which cooperate in pairs with the honing members, as will be described in more detail below. In an alternative embodiment, which has proved effective in maintaining the desired geometrical shape of the workpiece, a single sensor is provided for cooperating with each honing member, the sensor comprising a primary winding fed with alternating current and a secondary winding, both windings being placed on a magnetic yoke, the legs of which extend towards the workpiece, and the reluctance of which corresponding to the smallest value of the distance to the workpiece is small enough to couple to the secondary winding a voltage causing actuation of the magnetic valve. A multivibrator or trigger circuit may be connected to the input side of the relay to provide a threshold, so that no response will be obtained when the distance between the magnetic yoke and the workpiece is above the permissible limit value. In this type of sensor, the mutual spacing of the magnetic yoke legs is equivalent to a displacement of the point of disengagement from the midpoint of the honing member towards one end thereof.

Ifthe geometrical requirements are extremely stringent, it is advisable to dispose below the section covered by a honing member a pair of sensors, preferably of the'inductive type described, with a mutual spacing which is smaller than the axial length of the honing member, the latter being controlled so as to engage the workpiece when both sensors of the pair are at a minimum distance therefrom and to be disengaged when the distances of the sensors are different.

In order to enable honing of rods with different values of maximum diameter, it is necessary to provide means for adjusting the sensors radially with regard to the workpiece. Since the end surfaces of all sensors are placed in a straight line which is parallel to the axis of the workpiece irrespective of the distance of the sensors from the latter, it is possible to mount the sensors for simultaneous correction of the distance on a common rail running parallel to and at adjustable distance from the workpiece.

If a pair of sensors are provided for each honing member, the current supply circuit of the corresponding magnetic valve may comprise a section which is divided into two parallel branches, each of which has inserted therein a corresponding relay contact.

It was pointed out above that it is important for obtaining the exact geometrical shape of the stepwise transitions from a larger to a smaller diameter that the engagement of the honing members should take place, irrespective of wear, at the same points. If a recently replaced honing member is raised to the same height as another which has become shorter owing to wear, the latter has to move through a longer path before engagement occurs. Since the speed with which the honing members move downwards must be appreciably smaller than that of falling to provide smooth engagement, the time required for engaging a honing member shortened by wear is substantially longer. To obviate this delay, means are provided for maintaining the stroke of the honing member constant independently of the level at which engagement occurs. A stop is provided for limiting the stroke and to adjust automatically its positions according to the height of the honing member.

In an alternative embodiment, a hydraulic stroke limiting device may be provided comprising a storage device in the form of a spring-biased piston which is slidable in a cylinder and cooperating with a valve, preferably magnetic, which operates in synchronism with the magnetic valve controlled by the sensors. When the piston for actuating the honing members is raised, the storage device is filled with pressure medium, a drainage line thereof being closed by the magnetic valve. When the storage device has become filled, no further raising of the piston is possible. Not until the valve of the stroke-limiting device is in the inoperative position does an emptying of the storing device become possible. After this, the amount of pressure medium received by the storage device is proportional to the stroke of the piston actuating the honing members and the stroke is therefore independent of the degree of wear of the latter.

The invention will be described in more detail with reference to embodiments thereof shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic representation of the honing machine with the arrangement for automatically raising and lowering the honing members, presented in lateral view and with one of the rollers, which would obstruct the view of the workpiece, being omitted.

FIG. 2 is a section taken on line 11-11 of FIG. 1.

FIG. 3 is an alternative embodiment having a single sensor per honing member.

FIG. 4 shows in section a support for the sensors in the form of a pair of rails, one of which is displaceable relative to the other.

FIG. 5 is a section on line V--V of FIG. 4.

FIG. 6 shows schematically a hydraulic stroke-limiting device.

DESCRIPTION OF THE EMBODIMENTS As shown in FIGS. 1 and 2, a rod-shaped workpiece 13 is supported between a pair of rollers and 11, which are inclined relative to each other and are rotatable as shown by the arrow 12, the workpiece rotating in the opposite sense to the rollers, as shown by arrow 14 in FIG. 2, and receiving a forward feeding movement in the direction of arrow 15 (FIG. 1). Honing members 16 are in contact with the surface of workpiece 13 in positions corresponding to the largest diameter and are made to reciprocate in the axial direction of the workpiece. At the forward end, the workpiece exhibits a step or shoulder 17, behind which the diameter is substantially smaller. workpiece 13 is followed by a second workpiece, the front end 18 of which has a diameter corresponding to the smaller diameter of the preceding workpiece. Following this end is a step 19, followed by a section of larger diameter, on which the honing operation is to be performed. Between the two steps there is a section which can pass below a honing member only if the operating surface thereof has at least the same or, preferably, a distance from the axis of workpiece 13 larger than the diameter on which the honing is to be performed. This requires the honing member to be raised from the surface of the workpiece, which should preferably take place before the front edge thereof relative to the direction of feed coincides with the stepwise transition from larger to smaller diameter. The required length of the section of workpiece 13 which is covered by honing member 16 at the moment of being raised has to be ascertained by experiments for achieving optimal geometrical shape of the edge formed by the step.

An intermediate honing member 16' is shown in raised position. Honing members 16 and 16 are mounted on rods 20 of double-acting pistons 22, which are slidable in cylinders 21. A reciprocating motion as shown by arrows 15' is imparted to cylinders 21 to give honing members 16 the previously described reciprocating motion in the axial direction of the workpiece. Upward and downward movement of the pistons is obtained with the aid of a pressure medium under the control of a magnetic valve 23. Below workpieces 13 there are provided sensors 24 opposite to the sections covered by honing members 16 and 16. Sensors 24 are mounted on a rail 25, which is friction-fitted on a support 26 so as to be adjustable parallel to itself and radially to workpieces 13 to enable adjustment of the distance between the end surfaces of sensors 24 and the surface of the workpiece.

FIG. 3 shows a sensor which differs from the inductive sensors of the FIG. 1 embodiment in that its operation depends not on a variation of induction, but on a variation of reluctance. One sensor is provided for each honing member and comprises a U-shaped yoke 27 having its legs extending towards the workpiece. The yoke carries a primary winding 28 supplied with alternating current and a secondary winding 29. The current induced in the secondary from the primary is translated via an amplifier V and a diode bridge circuit rectifier G to a multivibrator or trigger circuit K, which responds at a predetermined current level to energize a relay 34 and open a normally closed contact 31. The amperage at which the multivibrator responds is inversely proportional to the magnetic resistance of the circuit of yoke 27. In the position illustrated in FIG. 3, the end surfaces of the magnetic yoke legs are opposite to the small diameter of the workpieces and the reluctance, owing to the larger air gap between the end surfaces and the workpiece, is large. Relay 30 then receives no current, the contact thereof is closed and magnetic valve 23 is inoperative. If the yoke legs are opposite to the large diameter of the workpiece, the magnetic resistance is minimal and the multivibrator supplies sufficient current for actuating relay l3 and contact 31.

If the FIG. 1 arrangement is modified to comprise only one sensor per honing member, which is positioned, as indicated in dash-dot lines in FIG. 1 at 24', at the midpoint of the section of the workpiece covered by the honing member, magnetic valve 23 is actuated by a single relay 30 for supplying voltage to the operating winding thereof. Valve 23 then switches from the inoperative position shown, in which pressure medium is supplied to the space above piston 22 and the honing member is pressed against the workpiece, to its operative position, in

which pressure medium is supplied to the space under the piston causing the honing member to be removed from the workpiece.

If two sensors 24 are provided for each honing member, for instance in the form of inductive sensors, which differ only in construction but not in function from those of the above embodiments, both sensors are disposed opposite to the honing member but slightly inwardly relative to the ends thereof. In this case, each one of the two contacts 31 of the relays is inserted in a corresponding one of a pair of branches into which a section of the current supply circuit of the magnetic valve is divided, whereby the winding of magnetic valve 23, which is spring-biased to the inoperative position, is energized only when both contacts are closed, and also, receives no current only in case both contacts are open as shown in FIG. 1.

FIG. 2 shows an arrangement for keeping the stroke of the honing member constant independently of the degree of wear thereof. The arrangement comprises a stop formed by a rod 32 in cooperation with a locking means in the form of a pivoted arm 33 urged into contact with rod 32 by a spring 34. Rod 32 tends to slide downward by gravity and follow the downward movement of locking arm 35 supporting the lower end of rod 32. Arm 35 extends through a slot in piston rod and is mounted at one end on a pivot 36 provided on rod 20. Locking arm 35 is biased to the position shown by any means known per se, such as a spring (not shown). If the radial dimension or height of the honing member is reduced owing to wear, locking arm 35 moves gradually downwards parallel to itself, supporting rod 32 when the honing member is lowered onto the workpiece. However, owing to the locking action of means 33, rod 32 cannot participate in upward movement of piston rod 20. This causes locking arm 35 to turn counterclockwise. The bottom surface of the slot in rod 20 accommodating arm 35 is inclined, as indicated at 37, allowing a small angular movement of arm 35. In the terminal position of arm 35 after this angular movement, it blocks further upward movement of piston rod 20. The stroke of the honing member therefore corresponds to a constant distance which is proportional to the maximum angular movement that can be performed by locking arm 35.

The constancy of the stroke can also be achieved by hydraulic means. The stroke limiting device of FIG. 6 comprises a magnetically controlled valve 44 and a pressure medium storage device 45. Line 43 for supplying pressure medium to the space above piston 22 (see FIG. 1) is divided into sections 43a and 43b. Section 43a is connected to magnetic valve 23 and section 43b to the space above the piston. The winding of valve 44 is connected in parallel to that of valve 23, so that the two magnetic valves operate in synchronism. In the illustrated inoperative position of valve 44, sections 43a and 43b are interconnected and since valve 23 is in the inoperative position shown in FIG. 1, pressure medium is supplied to the space above piston 22. If valve 44 switches to the operative position simultaneously with valve 23, line section 43b is connected to storage device 45. This device comprises a free piston 46, which is slidable in a cylinder 47 and urged upwardly against the biasing force of a spring 48 by the pressure medium when the latter is forced into the storage device via line section 43b and valve 44 upon a stroke performed by piston 22. If the storage device is full, i.e. piston 46 is in its uppermost position, the remaining pressure medium in the space above piston 22 blocks further upward movement of piston 22 in a similar manner to rod 32 of the mechanical stroke-limiting device of FIG. 2 in its cooperation with locking arm 35, and prevents further upward movement of piston 20. If magnetic valve 44 is reset to the inoperative position simultaneously with valve 23, line sections 43a and 43b are again interconnected, but storage device 45 is now emptied via a drain tube 49 when piston 46 is forced downwardly by spring 48. The amount contained in the storage device is therefore proportional to the stroke of piston 22. The stroke of the free piston 46 can be adjusted with the aid of a screw 50 so as to adjust the stroke of piston 22 to a desired value. A corresponding adjustment would be possible in the mechanically operating stroke limiting device of FIG. 2 only with the aid of complicated mechanisms, for it would require the turning angle of locking arm 35 to be adjustable, and to achieve this, a great number of mechanical parts would be necessary.

It was indicated above that the spacing of the sensors 24 corresponding to the same honing member must be found experimentally. This requires the spacing to be adjustable. An embodiment of supporting means for the sensors making possible such adjustment is shown in FIGS. 4 and 5 as comprising a pair of rails 38 and 39, rail 38 supporting those sensors 34 which are at the front end of the corresponding honing members and rail 39 those at the rear ends. Rail 38 is provided with a boring fitted onto support 26 and is secured thereto by means of a clamping screw. Rail 39 has a slot 40, through which extends a screw with its operating handle 41. The threaded portion of the screw engages a threaded boring provided in rail 38. By loosening of screw 41 and adjustment of rail 39 relative to rail 38, the spacing of the individual sensors of the pairs can be adjusted relative to each other, after which rails 38 and 39 are locked in position by tightening of the screw.

In the arrangement described, the sensors of rail 38 are not adjustable. Such adjustability can be achieved by making support 26 adjustable along a guide rail which is parallel to the axis of the workpiece and providing means for locking the support in adjusted position.

It is apparent from FIG. 2 that rollers 10 and 11 exhibit notches 42 at the location where sensors 24 extend into the space between them, these notches serving to prevent the rollers from magnetically influencing the sensors by coming too close thereto. For simplicity, these notches are not shown in FIG. 1.

That which is claimed is:

1. An arrangement for high-precision machining of workpieces comprising:

a pair of rollers adapted for rotation in the same sense and for supporting with longitudinal tangential contact workpieces in the form of rods having sections of different diameters, the axes of said rollers being disposed in planes defining an acute angle and intersecting along a line which is perpendicular to said axes for imparting longitudinal feeding motion to said workpieces,

honing members reciprocable longitudinally for machining the sections of said rods having the largest diameter,

pressure means for urging said honing members into contact with a workpiece,

sensor means for sensing sections of said workpieces of smaller diameter,

means responsive to said sensor means for increasing the distance of the honing members from the axis of the workpieces and maintaining the increased distance as long as said sections of smaller diameter are positioned opposite to said honing members,

said sensor means 24 being disposed in a position below that of the sections of said workpieces covered by the honing members 16 and 16 opposite thereto and in immediate proximity to the perimeter of the largest diameter section of a workpiece, said sensors being arranged in positions fixed independently of said diameters and being adapted to respond electromagnetically thereto.

2. An arrangement as claimed in claim 1, in which said sensor means 24 are disposed substantially below the position corresponding to the midpoint of sections of said workpieces 13 covered by said honing members 16, 16'.

3. In an arrangement as claimed in claim 2, comprising relays 30 responsive individually to said sensor means 24, each relay having a contact 31 thereof inserted in the current supply, a circuit for applying current to a magnetic valve 23 controlling the supply of pressure medium to pressure-responsive means for moving said honing members 16, 16' into and out of contact with a workpiece.

4. In an arrangement as claimed in claim 3, comprising an individual sensor for each honing member, said sensor having a Uoshaped magnetic yoke 27 having the ends of the legs thereof extending to a position corresponding to the proximity of the surface of a workpiece l3 and having a primary winding 28 to be supplied with alternating current and a secondary winding 29, the magnetic resistance of said yoke circuit for a minimum distance of said legs from the surface of a workpiece corresponding to a diameter to be machined being sufficiently small to cause a voltage to be induced in said secondary winding for energizing a corresponding relay 30 to actuate the magnetic valve 23.

5. An arrangement as claimed in claim 1, comprising a pair of spaced-apart sensors 24 disposed below each section covered by a honing member 16, 16, means for controlling said honing members so as to engage a workpiece 13 when said pair of sensors are at a minimum distance therefrom to disengage said workpiece when one of said pair is at a larger distance than the other.

6. An arrangement as claimed in claim 5, comprising relays 30 individually responsive to the sensors 24 of said pair and having contacts 31 thereof inserted in separate branches connected in parallel in a current supply circuit of a magnetic valve 23 responsive to said sensors.

7. An arrangement as claimed in claim 1, comprising a common rail 25 for mounting said sensors 24 thereon, said rail being parallel to the direction corresponding to the axis of a workpiece and adjustable in distance therefrom.

8. An arrangement as claimed in claim 1, comprising stop means 32 for limiting the stroke of said honing members 16, 16' and adapted to automatically adjust its position in response to the radial dimension of said honing member to cause the same to be raised in disengaging a workpiece by a constant amount independent of wear. 9. An arrangement as claimed in claim 1, comprising a hydraulic stroke-limiting means with a biased free piston 46 reciprocable in a cylinder 47 and a valve 44 for operation in synchronism with sensor-responsive magnetic valve 23.

10. An arrangement as claimed in claim 8, in which said stop means 32 are adjustable in the direction of engagement of said honing members l6, 16, comprising disengageable locking means 33 blocking movement of the stop means 32 opposite to said direction and a locking arm 35 pivotable by a predetermined amount in response to movement of the stop means in said direction thereby to limit the stroke of the honing member.

11. An arrangement as claimed in claim 5, in which the forward sensors of said pairs relative to the direction of feed are mounted on a rail andthe rearward sensors on another rail, said rails 38, 39 being mutually adjustable in the longitudinal direction and lockable in adjusted position. 

1. An arrangement for high-precision machining of workpieces comprising: a pair of rollers adapted for rotation in the same sense and for supporting with longitudinal tangential contact workpieces in the form of rods having sections of different diameters, the axes of said rollers being disposed in planes defining an acute angle and intersecting along a line which is perpendicular to said axes for imparting longitUdinal feeding motion to said workpieces, honing members reciprocable longitudinally for machining the sections of said rods having the largest diameter, pressure means for urging said honing members into contact with a workpiece, sensor means for sensing sections of said workpieces of smaller diameter, means responsive to said sensor means for increasing the distance of the honing members from the axis of the workpieces and maintaining the increased distance as long as said sections of smaller diameter are positioned opposite to said honing members, said sensor means 24 being disposed in a position below that of the sections of said workpieces covered by the honing members 16 and 16'' opposite thereto and in immediate proximity to the perimeter of the largest diameter section of a workpiece, said sensors being arranged in positions fixed independently of said diameters and being adapted to respond electromagnetically thereto.
 2. An arrangement as claimed in claim 1, in which said sensor means 24 are disposed substantially below the position corresponding to the midpoint of sections of said workpieces 13 covered by said honing members 16, 16''.
 3. In an arrangement as claimed in claim 2, comprising relays 30 responsive individually to said sensor means 24, each relay having a contact 31 thereof inserted in the current supply, a circuit for applying current to a magnetic valve 23 controlling the supply of pressure medium to pressure-responsive means for moving said honing members 16, 16'' into and out of contact with a workpiece.
 4. In an arrangement as claimed in claim 3, comprising an individual sensor for each honing member, said sensor having a U-shaped magnetic yoke 27 having the ends of the legs thereof extending to a position corresponding to the proximity of the surface of a workpiece 13 and having a primary winding 28 to be supplied with alternating current and a secondary winding 29, the magnetic resistance of said yoke circuit for a minimum distance of said legs from the surface of a workpiece corresponding to a diameter to be machined being sufficiently small to cause a voltage to be induced in said secondary winding for energizing a corresponding relay 30 to actuate the magnetic valve
 23. 5. An arrangement as claimed in claim 1, comprising a pair of spaced-apart sensors 24 disposed below each section covered by a honing member 16, 16'', means for controlling said honing members so as to engage a workpiece 13 when said pair of sensors are at a minimum distance therefrom to disengage said workpiece when one of said pair is at a larger distance than the other.
 6. An arrangement as claimed in claim 5, comprising relays 30 individually responsive to the sensors 24 of said pair and having contacts 31 thereof inserted in separate branches connected in parallel in a current supply circuit of a magnetic valve 23 responsive to said sensors.
 7. An arrangement as claimed in claim 1, comprising a common rail 25 for mounting said sensors 24 thereon, said rail being parallel to the direction corresponding to the axis of a workpiece and adjustable in distance therefrom.
 8. An arrangement as claimed in claim 1, comprising stop means 32 for limiting the stroke of said honing members 16, 16'' and adapted to automatically adjust its position in response to the radial dimension of said honing member to cause the same to be raised in disengaging a workpiece by a constant amount independent of wear.
 9. An arrangement as claimed in claim 1, comprising a hydraulic stroke-limiting means with a biased free piston 46 reciprocable in a cylinder 47 and a valve 44 for operation in synchronism with sensor-responsive magnetic valve
 23. 10. An arrangement as claimed in claim 8, in which said stop means 32 are adjustable in the direction of engagement of said honing members 16, 16'', comprising disengageable locking means 33 blocking movement of the stop means 32 opposite to said direction and a locking arm 35 pivotable by a pRedetermined amount in response to movement of the stop means in said direction thereby to limit the stroke of the honing member.
 11. An arrangement as claimed in claim 5, in which the forward sensors of said pairs relative to the direction of feed are mounted on a rail and the rearward sensors on another rail, said rails 38, 39 being mutually adjustable in the longitudinal direction and lockable in adjusted position. 